Fusion rates support wired allograft combined with instrumented craniocervical fixation in the paediatric population

All AA and OC fusions performed in consecutive pediatric patients in a 10 year cohort were reviewed in a tertiary referral clinic for complex spine conditions. The most common condition was a C1-C2 instability related to Down syndrome. All children except the one patient with a C1 fracture exhibited clinical pyramidal signs of spinal cord compression. Clinical data and details of surgery were gathered; clinical and radiological outcomes were retrospectively reviewed. All patients were subject to CT scan and if indicated a dynamic fluoroscopy at follow up. As this concerns a retrospective chart study, approval of the Medical Ethics Committee is not mandatory.

We did not employ neurophysiological monitoring. Internal rigid fixation was performed by the senior authors in all patients using a screw and rod system. When local anatomy allowed for placement of a screw in C1, this was the preferred treatment option. Either lateral mass screws were placed in C1, used in two patients (ID3 and ID12), or transarticular C1-C2 screws in three patients (ID2, ID3-r, ID10). If placement of a screw in C1 was considered unsafe due to small size of the C1 anatomy, a craniocervical construct was chosen, and the C1 arch was fastened to the rod with a titanium cable (8 patients). For C2 fixation, we used screw techniques depending on local anatomy: pars interarticularis screws (9/13), pedicle screws (1/13) (as defined by Benzel [5]), or transarticular screws (3/13), typically 3.5–4.5 mm in diameter and 12-18 mm in length. If indicated, a small-sized occiput plate was fixed on the planum nuchae using four bicortical screws close to midline and connected with titanium rods. In four patients (ID 6, 7, 9, and 10), instrumentation of C3 and C4 was performed.

We used a modified Gallie fusion technique. [23] Occipital bone surface, the posterior arch of C1, the C2 lamina, bilateral facet joints, and the spinous processes were decorticated with a high-speed drill before placing the allograft. Frozen allogeneic grafts were used as scaffold for bony fusion. Living donor femoral heads were employed, supplied by ETB-BISLIFE, a non-profit tissue institution (Galileiweg 8, Leiden, The Netherlands). A bone block was crafted to exactly fit the local anatomy using a bone rongeur and/or high speed drill. The monocortical bone block was carved from the femoral head, with a tight fit of the grafts spongious side to the posterior surface of the occiput and/or C1 posterior arch with a caudal notch to fit around the C2 spinous process. Using a Deschamps needle, a double titanium cable (Atlas Cable, Medtronic, Minneapolis, USA) was passed sublaminarly under the C1 arch (Fig. 1). Sublaminar wires under the C2 arch were not employed. In most patients, both cables were additionally guided around the rods of the screw and rod system bilaterally after which the cables were tensioned and crimped (Fig. 2). In this fashion, the C1 arch could be retracted posteriorly if indicated, and the resulting construct was considered stiffer including also C1 (Fig. 3). The cable was subsequently passed over the cortical side of the onlay bone block. Once the graft was tightly placed, the titanium cable was tensioned to 35 pounds and crimped on top of the bone block. Around the bone block graft, morcellized spongious graft was deposited, obtained from the remainder of the femoral donor head. In patient ID3, sublaminar wiring was not employed during the first surgical procedure, as the bone block seemed tightly fit between the occiput and C2 spinous process without wiring. In another two procedures (ID1 and ID2), only morcellized graft was inserted. Autologous bone marrow aspirate, aspirated from the patient’s iliac wing, was applied around the graft material in 4 patients. BMPs were not used (Table 1).

Patients underwent standard clinically examination at 8 and 26 weeks post-operatively. For confirmation of fusion, computed tomography was performed in all patients and flexion-extension radiographs of the cervical spine if indicated. Fusion was defined as cortical union of the allograft and central trabecular continuity as proof for a complete bony bridge [22] between the posterior arch of C2 and the occiput (OC fusion) or posterior arch of C1 (AA fusion). The fusion was assessed independently from radiologists by the senior authors. Once bony fusion was ascertained, this was defined as radiological endpoint, and no more CT scans were obtained.

We identified twelve pediatric patients with craniocervical instability who were treated with rigid posterior fixation and operated between 2006 and 2014. Mean age at surgery was 9.7 years (range 1–15 years), 25% of patients was female. All but one patient were over 5 years of age. All patients had instability of the C0-C1-C2 segment either as a direct result of their condition, or instability existed after surgery (e.g., tumor resection or transoral odontoid resection). Ten patients suffered from congenital malformations of the craniocervical junction: three in Down syndrome (with os odontoideum in one), two patients diagnosed with spondyloepiphyseal dysplasia congenital (SED), and the other patients were diagnosed with Larsen syndrome (n = 1), Marfan syndrome (n = 1), Arnold Chiari syndrome type 2 (n = 1), a syndrome caused by a de novo mutation in ZMYND11 [6] (n = 1), and a syndrome of unknown origin (n = 1). Two remaining cases suffered of acquired junctional instability: one due to traumatic fracture of C1 and one after transoral resection of a skull base chordoma. Transoral anterior decompression preceding the OC fixation was performed in 4 patients.

Median follow up imaging was 22 months (range 6–69 m). No post-operative complications of the posterior fixation procedure were noted. Median duration of admission was 6.6 days (range 4–11). Restriction of cervical motion by collar or halo frame in the post-operative period was not applied.

In the present cohort, 11/13 procedures resulted in a stable bony fusion; all primary surgeries that included a tightened wiring of allograft bone block resulted in bony fusion. Two of 13 occipitocervical fusion procedures resulted in a non-union (15%). Both non-unions occurred in patients without a wired bone block graft: patient ID3 showed a unilateral C2 screw breakage at follow-up imaging after 16 months as a result from persistent instability. A re-fixation was performed with allograft bone block, sublaminar wiring, and application of bone marrow aspirate, eventually resulting in a solid anterior and posterior C0–C2 fusion. In patient ID1, no bone block was placed. On follow-up imaging at 6 months, a stable position of the C1-C2 segment was seen, however, no bony union. Flexion-extension fluoroscopy shows no movement at follow-up time of 3 years; therefore, no re-intervention was indicated.